One of the most frequent failures encountered in encapsulated micro devices is the so-called open circuit which results from a break of the bonding wire between the circuitry. The breakage is primarily due to corrosion. This corrosion is initiated by the impurities in epoxy resins, such as halogen, which upon exposure to heat and moisture generate a corrosive acid.
Since the introduction of the low chloride epoxy resins, the wire bond failure due to the chloride impurities in the resin has become much less prominent than that due to the bromine from the fire retardant in the encapsulation formulation. Water extracts of molding compounds after high temperature storage have been found to contain bromide ion levels directly proportional to the bromine content in the molding compounds. A direct relationship between failure rate and bromine content in the molding compound has also been established.
It would therefore, be desirable to have available epoxy resins which when employed in curable formulations would have good thermal and hydrolytic stability to the molding formulation while providing fire retardancy properties.